Chapter 11 Muscular Tissue Flashcards
Skeletal muscle tissue
Locations: combined with connective and nervous tissue in skeletal muscle
Functions: moves or stabilizes the position of the skeleton
Cardiac muscle tissue
Location: heart
Functions: circulates blood, maintains blood pressure
Smooth muscle tissue
Locations: walls of blood vessels, digestive system, respiratory, urinary and reproductive organs
Functions: moves food, urine, reproductive secretions, regulates diameter of blood vessels
Excitablity
Responsiveness to chemical signals, stretch and electrical changes across the plasma membrane
Conductivity
Local electrical excitation sets off a wave of excitation that travels along muscle fiber
Contractility
Shortens when stimulated
Extensibility
Capable of being stretched between contractions
Elasticity
Returns to its original length after being stretched
Skeletal muscle
Voluntary striated muscle usually attached to bones
Striations
Altering light and dark transverse bands
Voluntary
Subject to conscious control
Endomysium
Connective tissue around muscle cell
Perimysium
Connective tissue around muscle fascicle
Epimysium
Connective tissue surrounding entire muscle
Sarcolemma
Plasma membrane of a muscle fiber
Sacroplasm
Cytoplasm of a muscle fiber
Myofibris
Long protein cords occupying most of sarcoplasm
Glycogen
Carbohydrate stored to provide energy for exercise
Myogoblin
Red pigment
Provides some oxygen needed for muscle activity
Multiple nuclei
Flattened nuclei pressed against the inside of the sarcolemma
Myoblasts
Stem cells that fused to form each muscle fiber early in development
Satellite cells
Unspecialized myoblasts remaining between muscle fiber and Endomysium
Where’s mitochondria in muscle fiber
Packed into spaces between myofibrils
Sarcoplasmic reticulum
Smooth ER that forms a network around each myofibril
Terminal cisterns
Dilated end-sacs of SR which cross the muscle fiber from one side to the other
T tubules
Tubular unfolding of the sarcoldmma which penetrate through the cell and emerge on the other side of
Triad
a T tubule and two terminal cisterns associated with it
Thick filaments
Made of several hundred myosin molecules
Thin filaments
Fibrous actin
Tropomyosin molecules
G actin
Troponin molecule
Elastic filaments
Titin
Runs through core of thick filament and anchor it to Z disc and M line
Provides overstretching
Helps position thick filament
Purpose of sarcoplasmic reticulum
-contains pumps moving calcium from sarcoplasm to SR
-calcium is essential and critical for muscle contraction
Contractile proteins
Myosin and actin do the work of contraction
Regulatory proteins
Tropomyosin and tropnin
-acts as switch determining when fiber can or cannot contract
Dystrophin
Important protein
-transfers forces or muscle contraction to tendon
A Band
Dark, anisotropic
-darkest part where thick filaments overlap the thin filaments
H Band
Middle of A band
-thick filaments only
M Line
Middle of H band
I Band
Light, isotopic
Z disc
Provides anchoring for thin filaments and elastic filaments
Sarcomere
From Z disc to Z disc
Why do muscle cells shorten
Because their individual sarcomeres shorten
Do thick or thin filaments change length during shortening
No, neither do
Sliding filaments theory
- H bands and I bands overlap
- Zones overlap and get larger
- Z lines approach each other
- A band remains constant
Describe a muscle
-A contractile organ
-attached to bones by tendons
-composed of fascicles of muscle fibers
-supplied with nerves and blood vessels
Describe a fascicle
-Bundle of muscle fibers within a muscle
-supplied by nerves and blood vessels
-enclosed in fibrous Perimysium
Describe a muscle fiber
-single muscle cell
-slender elongated thread like
-enclosed in its sarcolemma
-contains myofilements and proteins for contracting muscles
Describe a Myofibril
-bundle of myofilaments within a muscle cell
-surrounded by SR and mitochondria
-fills cytoplasm
Describe a Sacromere
-One Z disc to the other I. Organized patter
-hundreds of sacromeres make up one myofibril
Describe Myofilements
Protein strands that carry out the contraction process
Thick: composed mainly on myosin
Thin: composed mainly of actin
Motor unit
-One nerve fiber and all the muscle fibers innervated by it
-dispersed throughout muscle
-produces weak contraction over wide area
-effective contraction requires several motor units at once
Small motor units
-fine degree of control
- 3-6 muscle fibers per neuron
-eye and hand muscles
Large motor units
-more strength than control
-powerful contractions supplied by large motor units with hundrends of fibers
Somatic motor neurons
-nerve cells whose cell bodies are in the brain stem and spinal cord that serve skeletal muscles
-each nerve fiber branches out to multiple muscle fibers
-each muscle fiber is supplied by only 1 motor neuron
Synapse
Point where a nerve fiber meets its target cell
Neuromuscular junction
When target cell is a muscle fiber
Axon terminal
Swollen end of nerve fiber
-contains acetylcholine
Synaptic cleft
Gab between axon terminal and sarcolemma
How many NMJ per muscle fiber
1
What does nerve impulse cause
Causes synaptic cleft vesicles to undergo exocytosis releasing ACh into synaptic cleft
Basal lamina
Thin layer of collagen and glycoprotein separating Schwann cell and muscle cell from surrounding tissue
-contains AChE which breaks down ACh
Schwann cell
Envelopes and isolates NMJ
NMJ consists of
1, synaptic terminal of neuron
2, motor end plate
3, synaptic cleft
Voltage
A difference in electrical charge
Resting potential
-90mV
In a unstimulated cell:
-more negative ions inside membrane
-membrane is charged with negative resting potential
-excess sodium ions in ECF
-excess potassium ions in ICF
In stimulated cell:
-na gates open
-na flows into cell
-positive inside
Depolarization
Inside plasma membrane becomes positive
Repolarization
Plasma membrane becomes negative again
Impulse
Wave of excitation from cells
Spastic paralysis
A state of continual contraction of the muscles
Tetanus
Lock jaw
Form of spastic paralysis
Flaccid paralysis
Muscles are limp and can’t contract
Curare
Competes with ACh for receptor sites but does not stimulate muscles
Botulism
Type of food poisoning blocking release of ACh
Myasthenia gravis
Loss of ACh receptors at NMJ
Rigor mortis
Post mortem ATP production stops and membranes become leaky
-CA2+ leaks out of SR setting muscle contraction cycle in motion
-CA2+ activates myosin actin bridges
-No ATP for bridges
-lysosomes digest bridges
-hardening of muscles and stiffening of body after death
Excitation contracting coupling
Events that link the action potentials on the sarcolemma activation of the myofilements,
Preparing them to contract
Contraction
Step in which muscle fiber develops tension and may shorten
Relaxation
When stimulus ends, muscle fiber relaxes and returns to resting length
Excitation
Nerve action potentials lead to muscle action potentials
Activities at the neuromuscular junction
- Action potential at synaptic terminal causes exocytosis of ACh
2.ACh diffuses across synaptic cleft and binds to receptors causing release of Na+ - Sarcolemma generates action potential and AChE inactivates receptors
Muscle fiber contraction cycle
- Arrival of calcium
- Calcium binds to troponin
- Cross bridge formation
- Stored energy in myosin head releases and gos towards M line
- Cross bridge detachment
- Myosin reactivation
Length tension relationship
Amount of tension generated by a muscle depends on how stretched or shortened it was before it was stimulated
Threshold
Minimum voltage necessary to generate an action potential in muscle fiber and produce a contraction
Twitch
Quick cycle of contraction and relaxation when stimulus is at threshold or higher
Latent period
Brief delay between stimulus and contraction
Isometric muscle contraction
-muscle produces internal tension but external resistance
-stays the same length
Isotonic muscle contraction
Muscle changes in length with no change in tension
Immediate energy source
-short, intense activities
-myogoblin provides brief supply of oxygen
-phosphagen system utilizes creatine to regenerate ATP providing energy for around 6 seconds of high intensity exercise
Short term energy source
-muscles switch to anaerobic fermentation
-converts glucose to lactate for ATP production for 30-40 seconds
Long term energy source
-Relies on aerobic respiration providing ATP
-utilizing glucose and fatty acids
Muscle fatigue
Progressive weakness due to prolonged activity
Impairs muscle function
VO2 Max
-indicates maximum rate of oxygen consumption during intense exercise
-proportional to body size, peaks at age 20
-declines 15% per decade without active aerobic engagement
Excess post exercise oxygen consumption
-increased rate of oxygen intake following activity
-essential for recovery
Fast twitch fiber (type II)
-quick powerful bursts of energy
-thick and strong
-responsible for rapid movements
-rely on anaerobic metabolism
Slow twitch fibers (type I)
-adapted for endurance activities to resist fatigue
-maintains posture
-high density mitochondria, myoglobin and capillaries giving red appearance
Intermediate fibers (type IIA)
-exhibit both fast and slow twitch fibers
-provides balance for endurance and power
-common in animals more than humans
Muscular dystrophy
-muscle degeneration replaced with fat and scar tissue
-hereditary
-caused by mutation in dystrophin gene
Myasthenia gravis
-antibodies attack neuromuscular junctions
